If father is havig blood group O negative and mother is O positive, is it possible that the child has blood group of A+ ?

Not possible.

Blood group O is recessive ( Rh factors, +/-, mean nothing here )

If both parents are O this thin is the only cross as a recessive expression must be homozygous.

OO X OO
=========

So, only an O blood type ensues here. Or, typing errors were committed.

No. One party would have to be an A